The snappily named ISO 12647-2 (Graphic technology — Process control for the production of halftone colour separations, proof and production prints) is all about ensuring that the printed output matches the expectations of the print buyer and his service provider. Equally important is that those expectations can in some way be unambiguously expressed, numerically, using characterisation data, in effect ICC profiles. Part 2 (Offset lithographic processes) is the bit of the ISO 12647 series that matters most to offset printers, for both heatset web and sheet fed presses. And it is also the bestseller of the ISO graphics technology standards.
ISO 12647-2 is used all over the world and numerous certification bodies certify printing companies for compliance to this standard. The document provides values for various printing parameters that together make up a general printing condition. These parameters are the substrate condition, colour values and screening plus the Tone Value Increase (TVI previously known as dot gain) and the ink sequence. ISO 12647-2 was most recently updated in 2013, so experts in the ISO committee responsible for this work are gearing up for the next revision. So far so blah, but this next version will be a major move forwards with this document.
A matter of faith
One of the biggest sources of consternation in the application of ISO 12647-2 is disagreement between two important religions in the world of offset printing. Do you use Near Neutral Calibration (NNC) or TVI calibration? Different parts of the world prefer one or the other, however in tests conducted some years ago it was found that the two calibration methods yield very similar results, results close enough to be acceptable for most print buyers. Differences arise when different screening technologies are used, or different substrates. However adding the NNC method, which is the basis of the G7 certification programme and is already included in ISO 12674-2 in an Annex, is not just a matter of swapping the text from ISO 12647-2’s annex into the body of the document.
Why the two cannot sit side by side as options for calibration is not easy to say (see religion above). For example, several years ago the Ghent Workgroup (GWG) asked ISO via Technical Committee 130 (TC130 is responsible for most of the ISO standards used in print production) to suggest or create one single ICC profile suitable for sheetfed offset printing on quality coated paper stock. That request was never met, since it could not be agreed that using two different calibration methods would produce exactly the same results.
Engineers working on revision of ISO 12647-2 have come up with a different approach. Whilst using the same CIE L*a*b* based aim colour values as before, the objective is to clearly define the calibration method being used for a given print run, and communicate which Printing Condition (PC) is assumed, since this will point to which characterisation data set should be used and so which ICC profile to use. This should be do-able, and in fact reflects common day to day practise in print production all over the world. The two different calibration methods are both in widespread use, and none of the two is likely to go away.
The focus here is mainly on PC1 (coated stock). The other seven printing conditions will remain. In fact it’s likely that the standard will be expanded to support even more paper types and printing conditions. But expanding the number of paper types supported in ISO 12647-2 will never fully solve the problem of discrepancies in output produced using TVI or NNC. Different geographies have different preferences based on the options substrate manufacturers make available to them. This is why the standard allows a custom printing condition to be specified and agreed on between the print buyer and printer.
However you cannot bring together two different approaches without specifying how to measure colours accurately. The current thinking is to require the use of the M1 measurement mode, rather than just recommending M1 as is currently the case. The M1 mode requires that the spectrophotometer can measure a complete spectrum of light. Its light sources must be able to emit UV light, so that the photospectrometer can pick up Optical Brightening Agents (OBA). Obliging operators to measure in M1 mode would ensure consistency in the measurement results. However, if the paper doesn’t contain any OBAs, or only a very small amount, the M0 mode will still be allowed. And so will M2, if the OBA content is low.
Unified at last
With the revised ISO 12647-2 we should have a single unified ICC profile for coated paper when the updated version of ISO 12647-2 is published in the not so distant future. Actually no. It’s more likely that ICC profiles based on the Fogra 51 characterisation data set will continue to be preferred by printers favouring calibration based on TVI, while the GRACOL 2013 ICC profile will be used by printers calibrating according to the G7/NNC method. This profile is based on CRPC6, Characterized reference printing condition 6 in ISO/PAS 15339-2.
So what’s really new in the revised ISO 12747-2 and what has been the point of this revision exercise? The point is that it’s now been tested and proven that both methods will render an almost identical result, and both are valid, compliant to ISO 12647-2. And printers will have to comply to the same tolerances, no matter what calibration method is used. In that sense global printing will finally be unified, if not in the way for example GWG had once hoped.
ISO graphics technology standards are tools that can save a lot of effort and trouble and expense for printing companies. They are developed by a community of amazingly clever people, dedicated to helping to make print more beautiful, predictable, economic and consistent. But there is always room for one more on the bus, so if you are interested to join the ISO committee get in touch with your national standards body and take it from there to get involved. https://www.iso.org/members.html